(a) Field of the Invention
The invention relates to a liquid crystal display, a device modifying an image signal for a liquid crystal display, and a method of modifying an image signal.
(b) Description of the Related Art
A liquid crystal display, which is one of the most widely used type of flat panel displays, typically includes two display panels where field generating electrodes, such as a pixel electrode and a common electrode, are provided with a liquid crystal layer interposed therebetween. The liquid crystal display generates an electric field in the liquid crystal layer by applying a voltage to the field generating electrodes to determine orientations of liquid crystal molecules of the liquid crystal layer and control polarization of incident light, thereby displaying an image.
The liquid crystal display generally includes a pixel including a switching element, such as a thin film transistor (“TFT”), which is a 3-terminal element, and a display panel provided with display signal lines, such as a gate line and a data line. The thin film transistor serves as a switching element that transfers or interrupts data voltage transferred through the data line to a pixel according to a gate signal transferred through the gate line.
A liquid crystal capacitor includes a pixel electrode and a common electrode as two terminals thereof, and the liquid crystal layer interposed between the two electrodes serves as a dielectric material. A difference between a data voltage applied to the pixel electrode and a common voltage applied to the common electrode is represented as a charge voltage of the liquid crystal capacitor, i.e., a pixel voltage. Orientations of liquid crystal molecules vary depending on the magnitude of the pixel voltage, and as a result, polarization of light passing through the liquid crystal layer varies. The polarization variation is shown as a variation of transmittance of light by a polarizer attached to the liquid crystal display, and as a result, the pixel displays luminance corresponding to a gray of an image signal.
However, due to the response speed of the liquid crystal molecules, a predetermined time is required until the pixel voltage of the liquid crystal capacitor reaches a target voltage, which is a voltage used to acquire desired luminance, and the time is changed by a difference of the voltage previously charged in the liquid crystal capacitor. Therefore, for example, when a difference between the target voltage and the previous voltage is large, if only the target voltage is applied from the start, it may not reach the target voltage while the switching element is turned on.
The dynamic capacitance compensation (“DCC”) scheme has been proposed to improve the response speed of the liquid crystal using a driving method without changing the properties of the liquid crystal. Based on the fact that the charging rate becomes increases as the voltage at the liquid crystal capacitor increases, and in detail, the DCC typically reduces the time for the voltage charged in the liquid crystal capacitor to reach the target voltage by controlling the data voltage (in practice, it is a difference between the data voltage and the common voltage, and for convenience of description, the common voltage will be assumed to be 0 volt) applied to the corresponding pixel to be greater than the target voltage.